Variable resistor with vernier control



May 3, 1960 W. A. BARDEN ET AL VARIABLE RESISTOR WITH VERNIER CONTROL 2Sheets-Sheet 1 Filed April 25, 1958 -l 2 27 3| H 7 IO J 24 9 9 I8 24 A1/ 3P4, 228 25 /2 Z9 Z7 39 Wayne A..Evardan MEPVITLE.ATZETHETL y 3, 1960w. A. BARDEN ETAL 2,935,714

O VARIABLE RESISTOR WITH VERNIER CONTROL Filed April 25, 1958 2Sheets-Sheet 2 Wayne A. arden Mar-v21"; B. zsman as W AW United StatesPatent 2,935,714 VARIABLE RESISTOR wrrn VERNIER CONTROL Wayne A. Bardenand Mervin B. Arisman, Elkhart, Ind., assignors to Chicago TelephoneSupply Corporation, Elkhart, Ind., a corporation of Indiana ApplicationApril 25, 1958, Serial No. 730,965

4 Claims. (Cl. 338-157) This invention relates to variable resistors ofthe type used in radio and television apparatus, and has as its generalpurpose to provide a variable resistor or potentiometer which has anextremely fine adjustment.

In some of the more recent television receivers, the horizontaldeflection circuits require very fine adjustments. Heretofore thisrequirement has been met through the use of two separate variableresistors, connected in series, one of which provided the usualrelatively course adjustment of the controlled circuit and the other,which had a much narrower resistance range, provided the desired fineadjustment. Obviously, of course, if the first resistor were equippedwith a fine enough mechanical adjustment, the second resistor would notbe'required.

Means for efiecting fine or very close adjustment of the rotor of acontrol such as a variable resistor or condenser, are not broadly new.In the early days of radio, for instance, the knobs used to adjust thetuning condensers often incorporated gear reduction transmission meansthrough which manual actuation of the knob was translated into muchslower rotation of the condenser shaft.

In a very broad sense, the present invention follows this same approachin that it employs the principles of planetary gearing to obtain a ratioas high as 15 to 1 between the actuator of the control and its rotor,but where prior adaptations of the idea placed the gear reduction in theknob for the control or were otherwise extraneous to the control, thisinvention incorporates the transmission in the control itself and,moreover, does so in a way which is entirely consonant with theestablished requirements, both functional and structural, of variableresistors used in television and radio receivers. Among these, ofcourse, is the need for keeping the control small, avoiding an excessivenumber of piece parts, and enabling mass production of the control toassure low cost. a

With this general objective in mind, it is specifically an object of-thepresent invention to provide a variable resistor embodying means withinitself for producing very fine adjustment of the resistance itintroduces into a circuit in which it is connected.

Another object of the invention is to provide a high ratio dilferentialmotion transmitting connection between the actuating shaft of a variableresistor and is rotor which, though reliably effective to produce thedesired fine adjustment or traverse of the eontactor along theresistance path, nevertheless is impositive, so that despite the greatmechanical advantage inherent in the transmission, continued turning'ofthe actuating shaft after the contractor has reached one of its limitsof rotation will not damage the control.

Another specific object of this invention is to provide a variableresistor with a high ratio or vernier type drive transmission betweenits actuating shaft and eontactor which employs no gears, and which isso designed and constructed that essential elements thereof are Parts of'ice the elements already present in the control, to thus hold thenumber of piece parts to a minimum.

With these and other Objects in view which will appear as thedescription proceeds, this invention resides in the novel construction,combination and arrangement of parts substantially as hereinafterdescribed and more particularly defined by the appended claims, it beingunderstood that such changes in the precise embodiment of thehereindisclosed invention may be made as come within the scope of theclaims.

The accompanying drawings illustrate two complete examples of thephysical embodiments of the invention constructed according to the bestmodes so far devised for the practical application of the principlesthereof, and in which:

Figure 1 is a longitudinal sectional view through a variable resistorembodying this invention;

Figure 2 is a cross sectional view through Figure 1 on the plane of theline 2-2, but with a portion thereof broken away;

Figure 3 is a' perspective view of the cover of the control, viewing thesame from the inside and ready for assembly with the base of theresistor;

Figure 4 is an exploded perspective view of the rotor assembly of theresistor; and 1 Figure 5 is a view similar to Figure 1, but on asomewhat smaller scale and illustrating a slightly modified form of theinvention.

Referring now particularly to the accompanying drawings, the numeral 6designates the base of a variable resistor of the type commonly used inradio and television receivers. As such, the base is made of suitableinsulating material and, at its center, it has a mounting bushing 7fixed thereto and projecting axially from the front face thereof. Thisbushing, in addition to providing means for mounting the entire controlupon a suitable support, also'provides a hearing or journal for theactuating shaft 8 of the control. The shaft is thus constrained torotate about an axis perpendicular to the base and, in the preferredembodiment of the invention illustrated in Figures 1 to 4, inclusive, issecured against axial displacement in either direction by a pair ofconventional C-washers 9--9' mounted on the shaft, with the bearingportion 10 of the bushing received ,therebetween. Rearwardly of itsbearing portion 10 the bushing is counterbored as at 11, for a'purposeto be hereinafter described.

The rear face of the base has a resistance path 12 thereon arrangedconcentrically about the axis of the shaft. Although this resistancepath has been illustrated as an arcuate element separate from the basebut fixed thereto by means of end terminals 13, it could be provided inany other suitable way.

Also overlying the rear face of the base is a metal collector ring 14which is disposed concentrically within the arcuate resistance elementand, like the element, is held in place by means of its terminal 15.Since the manner in which the resistance path and the collector ring aremounted or arranged on the base forms no part Of this invention, thesefeatures have not been illustrated in detail. If more specificinformation is desired respecting these details, reference may be had toPatent No. 2,632,832.

As is customary in variable resistors or Potentiometers, the resistancepath and the collector ring have resilient contact fingers16 and 17respectively bearing thereon. Both of these fingers are carried by or,more correctly, are an integral part of a eontactor 18 stamped andformed of metal possessing suitable resilience. The eontactor is mountedon a eontactor carrier 19, sometimes referred to as a drive arm, whichis constrained to rotation about the axis of the shaft and is supportedagainst rearward axial displacement in exactly the correct position withrespect to the base to assure proper contact pressure between theresistance path and the contactor finger which rides thereon.

The manner in which the contactor carrier is mounted and supportedagainst rearward axial displacement, and more particularly the way inwhich it is driven, are important and significant features of thisinvention. Contrary to the conventional practice wherein the carrier isfixed to the shaft, the contactor carrier 19 is freely slidablyjournalled upon the rear portion of the shaft, being preferably providedwith a forwardly projecting hub portion 25) to provide a longer andmore. stable bearing on the shaft.

Rotation of the shaft is differentially transmitted to the contactorcarrier 19 through a transmission means on the order of a planetarysystem. This transmission means comprises a small diameter drivingelement 21 on the rear end of the shaft, the cylindrical outer surfaceof which provides an inner circular rotatable track 21a, a stationarycircular outer track 22 concentrically encircling the inner track, and aplurality of balls 23-three in the illustrated embodiment of theinvention-confined between these two tracks in frictional rollingengagement therewith. The outer stationary track 22 is formed by theinside surface of a frustoconical rearwardly projecting extrusion of therear wall of a generally cup-shaped stamped metal cover 24 like thoseusually provided in variable resistors of this type and which, as iscustomary, is secured to the base 6 to coact therewith in providing ahousing or enclosure for the instrumentalities of the resistor..

The balls 23 are held in place between the inner and outer tracks by thecontactor carrier 19, the rear face25 of which bears against the side ofthe balls substantially opposite the side thereof in contact with thestationary track. The contactor carrier 1% not only coacts with the twotracks to hold the balls in place, but also provides means for applyingthe rearward axial thrust of a spring 26 upon the balls. This spring 26is received in the counterbore 11 of the mounting bushing and isconfined between the bottom of the counterbore and the front of the hub26 on the contactor carrier.

Because of the truncated, conical shape of the stationary track 22, itfollows that a substantial part of the rearward axial thrust imposedupon the balls 23 by the spring 26- is converted into a radially inwardcomponent so that the balls have good frictional engagement not onlywith the stationary outer track 22 but also with the rotatable innertrack 21a.

Hence, upon rotation of the inner track 21a in consequence ofadjustment'of the actuator shaft, the balls rotate about their points oftangency with the rear face 25 of the contactor carrier, and suchrotation of the balls causes them to roll alongthe outer track 22 tothereby efiect orbital motion of the balls about the shaft. This orbitalmotion which is much slower than the rotation of the actuator shaft, istransmitted directly to the contactor carrier to effect the desired fineadjustment of the resistor.

While the frictional engagement between the balls and the contactorcarrier of itself serves as a motion trans mitting connection betweenthese parts, a more positive driving connection is desirable and, forthis purpose, the contactor carrier has a generally circular wall 27projecting from its rear surface 25, shaped on its inside to providethree pockets 28, one for each of the balls. The pockets are separatedfrom one another by lugs 29 angularly spaced apart slightly more thannecessary to accommodate the balls, so that the balls have a degree offreedom in their respective pockets to assure smooth operation. Ineffect, therefore, the contactor carrier forms a cage for the balls, sothat the carrier must move with the balls as they orbit about the shaft.

' Through proper selection for the angle of'the truncated conicalstationary track 22 and the strength of the spring 26, it is a simplematter to make the component of friction between the balls and thetracks sufficiently greater than the drag on the contactor resultingfrom the engagement of its fingers upon the resistance element and thecollector ring, to assure the described operation of the device.Nevertheless, since friction between the balls and the tracks isdepended upon to translate rotation of the actuator shaft intoadjustment of the contactor, the transmission means of this inventionhas an important advantage over a positive driving connection such aswould be provided by a gear train.

As in all variable resistors, the adjustment of the contactor isconfined to less than 360 degrees. This is done by the engagement ofstop abutments 3%) on the contactor carrier with a stationary stop 31 onthe cover. Because of the substantial mechanical advantage resultingfrom the relatively high ratio between the driving and driven elementsof the transmission, serious damage might be caused by continuedrotation of the shaft after the contactor reached one of its limits ofadjustment if torque were positively transmitted from the shaft to thecontactor carrier.

The present construction eliminates this possibility, and does sowithout incurring other objections.

As explained hereinbefore, the rear face 25 of the contactor carrierbears against the balls 23 and is thereby supported against rearwarddisplacement, as is also the contactor which is mounted on the carrier.The balls thus define the axial position of the contactor and determinethe contact pressure on the resistance path.

Though it is preferable to have the actuator shaft positively securedagainst axial displacement in either direction in the manner described,the shaft can be held against forward displacement by giving its rearend portion which provides the inner track 21a a spool shapedconfiguration, as at 32 in Figure 5. In this case the rearmost flange 33of the spool, being considerably larger in diameter than the inner track21a would collide with the balls and prevent forward axial shifting ofthe shaft. In other respects, the modified embodiment of the inventionshown in Figure 5 is the same as that described.

From the foregoing description, it will be readily apparent to thoseskilled in this art that this invention provides a variable resistorwith an adjustment fine enough to obviate the need for separate finetuning resistors as has been the practice in the past wherever thecontrolled circuit had to be very accurately and closely adjusted; andthat because of the novel manner in which the invention incorporates theplanetary principle into the driving connection between the actuatingshaft of the control and its contactor, the device of this invention hasthe salutary attributes of small overall size, low cost and reliableperformance.

What is claimed as our invention is:

1. In a variable resistor, the combination of: a housing having a frontwall; variable resistance mechanism in the housing comprising statormeans mounted on the front wall, rotor means adjacent to the front walland cooperable with the stator means, and an actuating shaft carried bythe housing for rotation on an axis perpendicular to the front wall, forimparting rotation to the rotor means, the shaft projecting through thefront Wall and having a rear portion thereof disposed rearwardly of therotor; means carried by the housing supporting the rotor for rotationcoaxially'of but relative to the shaft and for axial motion lengthwiseof the shaft; means on the housing providing a frusto-conical trackspaced rearwardly of the rotor, and spaced radially from but coaxiallyencircling said rear portion of the shaft, the smaller diameter portionof said frusto-conical track being rearmost; a plurality of ballsconfined in the space between the rear of the rotor, the frusto conicaltrack and the rear portion of the shaft; spring means carried by thehousing and exerting a rearward axial force upon the balls through therotor to maintain the balls substantially wedgingly confined in goodfrictional rolling engagement with the track and the rear portion of theshaft, whereby rotation is imparted to the balls by the shaft to causethe balls to roll along the track and travel orbitally relative to theshaft at a rate slower than'the rate of shaft rotation; and means on therear of the rotor engaging over peripheral portions of each of the ballsforwardly of the track to connect the rotor to the balls whereby therotor rotates with the balls as they orbit.

2. The combination set forth in claim 1 further characterized by thefact that the rotor is provided with a hub by which it is journaled uponthe actuating shaft for rotation relative thereto and for limitedsliding motion lengthwise thereof.

3. The combination set forth in claim 2, further characterized by thefact that said spring means comprises a helically coiled spring looselyencircling the shaft at a location ahead of the rotor, and confinedbetween the front of the rotor hub and a part fixed with respect to thehousing.

4. In a variable resistor, the combination of: a housing having spacedfront and rear walls; an actuating shaft supported by the housing forrotation on an axis normal to and substantially centered with respect tosaid walls, said shaft projecting through the front wall and having arear portion adjacent to the rear wall of the housing; an arcuateresistance path on the rear of the front wall, concentric to the shaftaxis; means on the rear wall of the housing defining an annular frustoconical track concentrically surrounding said rear portion of the shaft,the smaller diameter portion of said track being rearmost; a rotatablecontact carrier in the housing having spring contact means on one facethereof; means carried by the housing mounting the carrier for rotationconcentrically with and relative to the shaft and for axial motion alongits axis, with said face of the carrier opposing the front wall of thehousing and its spring contact means in engagement with the resistancepath on said front wall to traverse the same during rotation of thecarrier; 2. plurality of balls confined axially between said frustoconical track and the rear of the carrier, and confined radially betweenthe track and said rear portion of the shaft; spring means exertingrearward axial force on said balls through the carrier to maintain theballs substantially wedgingly confined between and in good frictionalrolling engagement with the track and said rear portion of the shaft,whereby rotation of the shaft causes the balls to roll orbitally alongsaid track at a rate slower than the rate of shaft rotation, and wherebythe balls define the rearmost position of the carrier in the housing andthus serve to hold the spring contact means on the carrier in pressureengagement with the resistance path; and means on the carrier projectingrearwardly therefrom and engaged between said balls to constrain thecarrier to rotate with the balls as they orbit;

References Cited in the file of this patent UNITED STATES PATENTS1,995,171 De Tar Mar. 19, 1935 2,192,084 Kamenarovic Feb. 27, 19402,521,585 Kurtz Sept. 5, 1950 2,724,034 Altieri Nov. 15, 1955 2,789,191Arisman Apr. 16, 1957

